The present invention relates to a steel sheet and strip (hereinafter called as sheet) having good paint adhesion and the process for producing it.
Conventionally, the phosphate treatment has been often used for the purpose to improve the paintability of a steel sheet itself.
Further, plated steel sheets, including tin-, zinc- and aluminum-plated and TFS-CT, have been recognized advantageous for protecting the base metal material in various applications. More particularly, the role of the plating layer is twofold; one is to protect the base metal from corrosion, and the other is to give paintability to the material when it is used as painted. Of course the painted layer on the plated metal contributes to protect the base metal.
However, such chemical treatment as mentioned above to produce plated steel sheets requires complicated processes of the treatment and highly skillful technics as well as proper disposal of exhaust liquid and the equipments for the treatments. Hence, increased production cost is encountered with. Further, the products thus prepared are not always sufficiently paintable.
The present invention has its object to provide a steel sheet having more excellent paintability than that of the conventional phosphate treated steel sheets and that of the conventional plated steel sheets.
More particularly, the present invention has made it possible to provide at much less cost those steel sheets having the paintability well comparable with or superior to that of the conventional products. For example, a simple supplementary treatment according to this invention which is additionally applied to a conventional plate steel sheet can produce remarkable improvement in paintability, and thus raise the commercial value of the same.